The neurological mutants of mice are valuable tools which can help to unravel the complexities of nervous system development in mammals. My work is focused on understanding the role of the genome in cerebellar development. To this end I concentrate on three murine mutants each of which compromises development of the cerebellar cortex at different times and in different ways. The strategy is that much as biochemists rely on many mutants upsetting a single metabolic pathway to aid in its study, so too, analysis of developmental pathways will also benefit from a series of mutants. My approach is three-fold. The use of quantitative techniques reveals subtle changes in number or size of cells which can be as important as their presence or absence. Constructing mutant yields (reversibly) wild-type chimeric mice offers a powerful extension of the conventional genetics by providing mosaic nervous systems composed of mutant and wild-type cells in constant juxtaposition. Finally, histochemical staining of developing mutant and wild-type cerebellum with labeled plant lectins reveals the carbohydrate "signature" of the developing cerebellum and how this pattern changes in the mutants.